Rotating construction laser with a dual grade mechanism

ABSTRACT

A rotating construction laser includes a laser core module with a laser unit for emitting a laser beam and rotation means for rotating the laser beam around an axis of rotation defining a laser beam plane. The rotating construction laser is provided with an outer pivoting mechanism attached to the laser core module, the outer pivoting mechanism being operable to tilt the laser core module around an X-axis as a first axis of rotation and around a Y-axis as a second axis of rotation. The rotating construction laser further includes a dual grade mechanism with a first level sensor operable to indicate a rotation of the laser core module around the X-axis and a second level sensor operable to indicate a rotation of the laser core module around the Y-axis. Both level sensors can be operated mutually independent.

This application claims priority to European Patent Application No.EP09177262, filed on Nov. 26, 2009, the contents of which are herebyincorporated by reference herein.

The invention relates to a rotating construction laser comprising alaser core module with a laser unit for emitting a laser beam androtation means for rotating the laser beam around an axis of rotationthus defining a laser beam plane. The rotating construction laser isprovided with an outer pivoting mechanism attached to the laser coremodule, the outer pivoting mechanism being operable to tilt the lasercore module around an X-axis as a first axis of rotation and around aY-axis as a second axis of rotation. The rotating construction laserfurther comprises a dual grade mechanism with a first level sensoroperable to indicate a rotation of the laser core module around theX-axis and a second level sensor operable to indicate a rotation of thelaser core module around the Y-axis.

The invention also relates to a method of calibration of the dual grademechanism and a method of generating a pre-defined laser beam plane forlight emitted by the rotating construction laser according to theinvention.

BACKGROUND

Rotating construction lasers are well known in the prior art. Forexample, in U.S. Pat. No. 7,370,427 a construction laser with at leastone rotating laser beam defining a laser beam plane is described. Theconstruction laser has a laser unit that is tiltable relative to ahousing around at least one swiveling axis. The construction laserincludes at least one level sensor which is sensitive to rotationsaround the swiveling axis for a highly precise orientation to thegravitational field. The device further includes one tilt sensor whichis sensitive to rotations around the swiveling axis for directmeasurement of an inclination angle relative to the gravitational field,with less resolution than the level sensor, but with a broader angularrange that can be measured.

As a disadvantage of this embodiment, two sensors, a level sensor and atilt sensor, are needed to measure tilt around one axis with anacceptable degree of accuracy. Furthermore, the laser beam unitperiodically needs to return to its level position for recalibrating thetilt sensor.

WO 2008/052590 discloses a device for indicating a grade, for example inconstruction applications, using a laser beam. The laser beam is emittedfrom a laser unit to a desired direction having a grade angle withregard to the level angle. A level sensor is provided for adjusting thelevel angle and a grade sensor is provided for indicating a grade angleon the basis of the level angle from the level sensor. Thus, again twosensors are needed to correctly indicate the grade with respect to oneaxis of tilt.

According to U.S. Pat. No. 5,485,266, fixed tilt detectors are fixed inplanes crossing perpendicularly to each other of a shaft center of alaser projector, and tilting tilt detectors are mounted on a plate whichis tiltable with respect to the shaft center of the laser projector. Thelaser projector is level in such a manner that the fixed tilt detectorsindicate horizontal direction. The tilting tilt detectors are alignedwith the fixed tilt detectors and indicate a horizontal direction. Thus,a horizontal reference plane is obtained. The tilting tilt detectors aretilted with the fixed tilt detectors as a reference and the laserprojector is leveled so that the tilting tilt detectors indicatehorizontal direction. Thus, a reference plane tilted at an arbitraryangle is obtained.

This device also requires multiple tilt sensors.

In the prior art cited above, two tilt sensors are usually used formeasuring the tilt of one axis of tilt of a rotating construction laserwith high accuracy. One of these sensors is a level sensor which is ofvery high precision and very limited measurement range and typicallyused to calibrate the grade sensor or tilt sensor, which has a broadermeasurement range, but is less precise.

In U.S. Pat. No. 5,852,493 a self-aligning laser transmitter having adual slope grade mechanism is disclosed. The laser transmitter includesa light source coupled to a frame which is suspended from a gimbalmechanism. The gimbal mechanism and the frame are coupled to a rotatablebase. X and Y axes levelling devices are coupled to the gimbal mechanismand the frame to level the light source. A grade arm having two levelsensors mounted at ninety degrees to one another is coupled to theframe. The grade arm is pivoted along the X or Y axes by a grade armpivoting device. The X and Y axes leveling devices reposition the lightsource so that the level sensors are level thereby introducing a slopeto the light source corresponding to the amount of pivot of the gradearm. The base may be rotated for a dual slope capability.

In this embodiment only two level sensors are used which, however, aremounted to the same grade arm. Consequently, upon a tilt of the gradearm caused by actuation of the X and Y axes levelling devices both levelsensors are affected simultaneously. Hence, a precise calibration of thelevel sensors with regard to the X and Y axes is difficult. Typically acalibration with regard to either the X or the Y axis will be lessprecise than the other one.

In US 2008/0297921 a device for tilting the optical axis of a laseroptical system is disclosed. Two tilt sensors are provided which aremounted on a common platform at an orientation of 90° with respect toeach other. A gimbal mechanism supports tiltably the laser core module,comprising the laser light source and the beam-forming optical system ofthe laser. The gimbal mechanism also acts on the common platform of thetwo tilt sensors. Consequently, actuation of the X and Y axes levellingdevices does affect both level sensors simultaneously also in thisembodiment, again resulting in difficulties for a calibration of thelevel sensors with regard to tilting of the laser core module around theX and Y axes.

SUMMARY

It is an objective of the present invention to provide a rotatingconstruction laser with a simplified grade mechanism. It is a particularobjective of the invention to provide a grade mechanism using only onesensor per tilt axis and allowing the implementation of low-complexsensors for grade measurements. Simultaneously, the design of the grademechanism should allow for easy and precise calibration of the sensors.Another objective of the invention is to provide a method forcalibration of grade mechanism for a rotation construction laseraccording to the invention.

These objectives are achieved by the subject matter of the independentclaims. Further advantageous embodiments of the invention are describedin the dependent claims.

The rotating construction laser according to the invention comprises alaser core module and an outer pivoting mechanism attached to the lasercore module. The laser core module includes a laser unit for emitting alaser beam and rotation means, like e.g. a rotating prism, for rotatingthe laser beam around an axis (Z) of rotation thus defining a laser beamplane. The outer pivoting mechanism is operable to tilt the laser coremodule around an X-axis as a first axis of rotation and around a Y-axisas a second axis of rotation, the X-axis and the Y-axis typically beingperpendicular to each other.

Furthermore, the inventive rotation construction laser is provided witha dual grade mechanism comprising a first level sensor operable toindicate a rotation of the laser core module around the X-axis and asecond level sensor operable to indicate a rotation of the laser coremodule around the Y-axis. The first and the second level sensors aredesigned to detect balance with respect to gravity. The two levelsensors are individually attached to the laser core module, separatelyfrom one another. This ensures that really rotations or tilt of thelaser core module are detected and not, for example, deformations of anyintermediate connecting parts. According to the invention, the firstlevel sensor is rotatable around a third axis of rotation assigned tothat first level sensor, and the second level sensor is rotatable arounda fourth axis of rotation assigned to that second level sensor, rotationof the individual level sensors around their assigned axes beingmutually independent. Due to the mutually independent rotation of thelevel sensors around their related swivelling axes, any calibrationerrors will typically be equally small. The sensors may be attached bymeans of a pivot bearing directly to the laser core module. The levelsensors may also be mounted on a pin which is pivotably attached to thelaser core module, or any other known technique for pivotable connectionof the level sensors with the laser core module may be utilized. Therelated axis of rotation is determined by the specific mechanicalrealization of the connection of the level sensors with the laser coremodule.

Preferably, the axes of rotation for the level sensors are oriented inparallel to the X- and Y-axis of the outer pivoting mechanism. Thereby,the axis of rotation for the first level sensor may be connected to theX-axis of the outer pivoting mechanism for tilting the laser core modulein one direction, and the axis of rotation for the second level sensormay be connected to the Y-axis of the outer pivoting mechanism fortilting the laser core module in another direction. In particular, theaxis of rotation for the first level sensor may be oriented coaxiallywith the X-axis and the axis of rotation for the second level sensor isoriented coaxially with the Y-axis of the outer pivoting mechanism.

Accordingly the swivelling axes of the level sensors are preferablyoriented perpendicular to one another.

In an advantageous embodiment, the axes for rotation of the levelsensors pass through the centres of mass of the related level sensors.It is further advantageous if the level sensors have an elongate,barrel-type shape with a longitudinal axis, corresponding to the sensororientation of rotational sensitivity, oriented perpendicular to theaxis of rotation of the related level sensor. Symmetry of the levelsensor with respect to its axis of rotation is preferred in order toavoid effects of rotations around the related axis on the reading of thesensor.

The level sensors may be provided as bubble vial sensors or spirit vialswith a liquid in a receptacle. Based on said symmetric mounting of thelevel sensors, it is ensured that the bubble will be kept in the centerwith respect to their longitudinal axes. For the purposes of thisinvention, the level sensors are not necessarily provided as tiltsensors that can measure inclinations over a large measurement range,but as sensors with highly precise reading of deviations from theirbalance with respect to gravity, also known as detection of truehorizon, with a typical measurement range of about 1° or less tiltdeviating from balance. Such level sensors have been commonly used inself-levelling construction lasers where only indication of truehorizon, i.e. balance with respect to gravity, is required.

For precise, automated level measurements and adjustments it ispreferred that the level sensors are provided with an opto-electronicreadout system. The opto-electronic readout system may comprise a lightsource, preferably a laser diode or a light-emitting diode (LED),illuminating the liquid enclosed together with the bubble in the levelsensor. The light passing through the sensor and being deviated indifferent manners by regions filled with liquid and regions occupied bythe bubble in the sensor is detected by a light-sensitive device like aphotodiode or a one- or two-dimensional diode or CCD array capable ofdetecting deviations from a symmetric distribution of the transmittedlight. Any deviation from a symmetric transmitted light distribution maybe scaled according to a requested resolution.

In an advantageous embodiment rotations around the swivelling axes ofthe level sensors are actuated by a mechanical drive system comprising abearing system and a motor connected to the axis of rotation for therelated level sensor. The mechanical drive system can be attacheddirectly onto the axis of rotation, or it could be connected to theswivelling axis by a lever arm with a linear drive mechanism such as alead screw, or any other variations of the drive mechanism may beutilized. The motor, typically an electric motor, may be operated by acontrol unit.

It is further preferred that the mechanical drive system is providedwith a feedback mechanism for recording and monitoring motor-actuatedrotation of the swivelling axis. The feedback mechanism may comprise anoptical encoder or any adequate detection device like a linear sensorattached between level sensor and the laser core module operable torecord the actuation of the swivelling axis scalable to an angle ofrotation of the swivelling axis. Alternatively or additionally, thefeedback mechanism may comprise a rotary optical encoder.

In an advantageous embodiment, the electric motor and the feedbackmechanism are operated by the control unit according to a closed-loopprinciple, i.e. information/data for motor actuation sent by the controlunit to the electric motor and positional data received by the controlunit from the feedback mechanism are correlated. If, for example, theelectric motor is provided as a stepper motor, a number of steps of themotor can be translated into a corresponding angular rotation of theswivelling axis. The advantage of such a closed-loop principle ofoperation is that the correlation between angular position of theswivelling axis and the operating position of the motor is maintained atleast as long electric power is not interrupted.

The mechanical drive system may also be operated without feedbackcontrol or following an open-loop principle of operation, however uponcompromising the advantage of high repeatability and accuracy resultingfrom closed-loop operation under feedback: When using a stepper motorfor axis actuation, steps can be lost because of mechanical shock orfailure in the electronics. When operated according to an open-loopprinciple, information about such a loss of motor steps cannot befurther correlated with the actual axis position.

It is also advantageous if also the outer pivoting mechanism for tiltingthe laser core module is controlled by the control unit.

In another advantageous embodiment, the rotating construction laser isprovided with a storage medium and a calibration data table stored inthe storage medium. The calibration data table of this embodimentincludes the following entries:

1. A first set of calibration data for a first calibration pointobtained with the laser core module being mounted on an XY-axes tilttable with defined first values of tilt around the X-axis and theY-axis;

2. a second set of calibration data for the first calibration pointobtained after activation of the mechanical drive system for the axes ofrotation for the level sensors in order to rotate the level sensors intobalance with respect to gravity, the motor-actuated rotation of the axesuntil reach of balance of the level sensors with respect to gravitybeing recorded by the feedback mechanism and stored in the storagemedium as data equivalent to angular rotations around the X-axis and theY-axis, as the second set of calibration data.

The calibration data table may contain corresponding first and secondsets of calibration data for a second calibration point and, ifnecessary, for still further calibration points. Usually, thecalibration data table will comprise data for calibration points atseveral tilt positions thus representing a two-dimensional mesh ofcalibration points.

In a typical mode of operation, for generating a pre-defined laser beamplane, with a predefined tilt with respect to a horizontal plane, i.e.with a predefined tilt of the laser core module around the X- and theY-axis, the first and the second level sensor are first rotated relativeto the core module around their related third and fourth axis ofrotation by pre-set angular amounts, dependent on the pre-defined laserbeam plane. Then the laser core module is rotated by the outer pivotingsystem around the X- and Y-axis until reach of balance of the first andsecond level sensor, reach of balance being indicated by signal readoutof the first and second level sensor corresponding to true horizonposition.

In a preferred mode of operation of an automated system, the dual grademechanism of the rotating construction laser having been calibrated, auser will enter values for requested tilt of the laser core modulearound the X- and Y-axis into a computer system operating the rotatingconstruction laser, these values being supplied to the control unit.

The control unit will actuate the motors for rotating the level sensorsaround their related swivelling axes by angular amounts equivalent tothe preset values of tilt of the laser core module around the X- and/orY-axis. The amounts for rotation of the level sensors around the thirdand fourth swivelling axis may be retrieved from a stored calibrationdata table. However, also any other type of calibration of rotationsaround the axes holding the level sensors scaled to angular rotation maybe utilized (e.g. rotations of a lead screw). When the pre-definedpositions of the level sensors are reached the control unit 25 willactuated the outer pivoting system and rotate the laser core modulearound the X- and Y-axis until balance of the level sensors is reachedagain. Thereby, signals of the level sensors are acquired by theassociated opto-electronic readout system and fed to the control unitwhich maintains rotation of the laser core module until signal readoutindicating true horizon position of both level sensors is reached. Thus,a pre-defined tilted laser beam plane for light emitted by the rotatingconstruction laser is generated.

As a special positioning of the laser core module, a so-called lay-downfunctionality can be performed if rotation of the laser core modulearound the X- or the Y-axis by 90° is prompted. For that purpose,initially either the first or the second level level sensor is rotatedrelative to the core module around the related third or fourth axis ofrotation by an amount according to a 90° turn whereas the other levelsensor is maintained in a 0° turn position. Then the laser core moduleis rotated around the X- and/or Y-axis until reach of signal readout ofboth the first and second level sensor corresponding to true horizonposition. Typically, this is performed in two steps. First, the lasercore module is turned by about 90° manually, followed by fine-adjustmentusing rotation actuated by the outer pivoting system. However, if theouter pivoting system is operable over such a large range up to 90°angular rotation, also the complete step of 90° rotation may beperformed under control of the outer pivoting system. In this way, avertical laser beam plane is generated.

The described dual grade mechanism is always capable to restore thelaser core module with the associated level sensors in a predefinedposition with respect to the horizontal force if, e.g. by moving thesystem, balance with respect to gravity (i.e. true horizon position ofthe level sensors) has been lost: Because of the known relationshipbetween the setting of the X- and Y-axis of the outer pivoting mechanismand the positioning of the swivelling axes of the level sensors,deviations of the reading of the level sensors from true horizon readingare registered, and the laser core module is re-adjusted by tiltingaround the X- and Y-axis, until readout of the level sensor signalscorresponding to their true horizon position is reached again. In thisway the rotating construction laser with the dual grade mechanismaccording to the invention is provided with an automatic re-adjustmentfunctionality.

In an embodiment for basic requirements, the rotating construction laseris provided as a self-levelling true horizon construction laser androtation of swivelling axis of the level sensors and/or an optionalcalibration of the level sensors is performed manually without operationunder an electronic control.

However, it is preferred that a rotation of the level sensors around therelated swivelling axes is actuated by a mechanical drive system,comprising a bearing system and a motor, connected to the axes ofrotation, as described before.

A further subject of the invention is a method of calibration of a dualgrade mechanism for a rotating construction laser. Different types ofcalibration hardware can be utilized, and the inventive method is notlimited to the specific hardware configuration disclosed in thefollowing.—The essential steps of the inventive calibration method areas follows:

As a first step, the laser core module is mounted onto a two-axes tiltsystem, such as an XY-axes tilt table, as a calibration standard device.Preferably, for the calibration procedure a high-accuracy tilt table isused. The tilt table itself is calibrated for zero-tilt with respect tothe X-and Y-axis for true horizon position.

As a second step, for generating data for a first calibration point, thetilt table is adjusted at a first defined pair of values for tilt aroundthe X- and the Y-axis. These XY-tilt values are recorded as a first setof calibration data for the first calibration point.

Then, as a third step, the level sensors are rotated around theirrelated swivelling axes into balance with respect to gravity,corresponding to “true horizon” orientation of the level sensors. Incase of a bubble vial sensor with at least one transparent window thisposition is indicated by location of the bubble in the middle of thewindow. The amount of rotation around the swivelling axes of the levelsensors until reach of balance with respect to gravity is recorded forthe rotations of both level sensors as a second set of calibration datafor the first calibration point. This second set of calibration data isan equivalent to the first set of calibration data for angular tilt ofthe X- and Y-axes away from true horizon position of the XY-tilt table.

The third step of the calibration method may be performed by manual ormotor-actuated rotation of the swivelling axes of the level sensors andreading/manual recording of a scale attached to the axes showing theperformed angular rotation.

However, it is preferred that the rotation of the swivelling axes iseffected by means of an associated mechanical drive system comprising abearing system and a motor connected to the respective axis of rotationfor a level sensor. The mechanical drive system may be attached directlyonto the axis of rotation, or it could be connected to the swivellingaxis by a lever arm with a linear drive mechanism such as a lead screw,or any other variations of the drive mechanism may be utilized. Themotor, typically an electric motor, may be operated by a control unit.

It is further preferred that the mechanical drive system is providedwith a feedback mechanism for recording and monitoring motor-actuatedrotation of the swivelling axis. The feedback mechanism may comprise anoptical encoder or any adequate detection device like a linear sensorattached between level sensor and the laser core module operable torecord the actuation of the swivelling axis scalable to an angle ofrotation of the swivelling axis.

In this preferred embodiment of the calibration method, the feedbackmechanism provides the data for recorded motor-actuated rotation of theaxes as data equivalent to angular rotations around the X-axis and theY-axis, as the second set of calibration data for the first calibrationpoint.

Steps 2 and 3 of the calibration method may be repeated for seconddefined values of tilt around the X-axis and the Y-axis in order toobtain first and second sets of calibration data for a second point ofcalibration, and optionally steps 2 and 3 may be further repeated forobtaining sets of calibration data for still further calibration points.

For the special situation of zero-tilt around the X- and the Y-axis, thetrue horizon position of the level sensors, corresponding to theirbalance with respect to gravity, is defined.

The calibration data may be stored in a calibration data table. Thecalibration data table may be stored in a storage medium included in theinventive dual grade mechanism. The calibration data table may also befirst stored in a storage unit of the calibration standard device andthen be transformed into an adequate format for a calibration data tableto be made available for the laser control unit of the rotatingconstruction laser.

BRIEF DESCRIPTION OF THE FIGURES

It is pointed out that the specific advantageous embodiments of thevarious aspects of the invention disclosed above can be freely combinedto further embodiments within the scope of the invention.

The invention will further be explained in detail by referring toexemplary embodiments that are accompanied by figures, in which:

FIG. 1 and FIG. 2 show cross-sectional views of a possible embodiment ofa rotating construction laser provided with a dual grade mechanismaccording to the invention.

FIG. 3 and FIG. 4 show simplified illustrations of a rotationalconstruction laser according to the invention provided with a dual grademechanism.

FIG. 5 a and FIG. 5 b illustrate the indications of bubble vial sensorsas an example of level sensors upon rotation around one swiveling axis.

DETAILED DESCRIPTION

In FIG. 1 and FIG. 2, a rotating construction laser 1 is shown in twoviews—one from the front and one from the right hand side. Theconstruction laser 1 comprises a base 2 in form of a housing. A laserunit 3—as a means for generating a laser beam plane—is pivotably mountedto the base 2 using a pivoting system 4 that may be a spherical joint ora gimbal. The pivoting system 4 allows the laser unit 3 to swivel aroundan X- and a Y-axis—and thus to be tilted in two directions. The laserunit 3 comprises a hollow axle 5 and a head assembly 13 including anoptically transparent hood 14 that is rotatably around an axis 18mounted to the axle 5 using two bearings 15, 16. The pivoting system 4is attached to the axle 5 approximately at midsection. The axle 5 has alower end (not shown) and an upper end 7. A laser collimator unit (notshown) is located in the interior of the hollow axle 5 at the lower end.The laser collimator unit comprises a laser diode and a collimator (bothnot shown). The laser collimator unit generates a collimated laser beam11 that is directed along a center line of the axle 5 which isconcentric with the axis 18 towards the head assembly 13. A laser beamredirector 17 in the form of a prism is integrated into the hood 14. Thelaser beam redirector 17 changes the direction of the laser beam 11 byan angle of 90°. Since the laser beam redirector 17 is rotated with thehood 14, a laser beam plane is generated in which the laser beam 11rotates around the axis 18 of rotation. Typically, the hood 14 isrotated at a speed of several thousand revolutions per minute (rpm).

In the embodiment illustrated by FIG. 1 and FIG. 2, level sensors 20 a,20 b are mounted on axes of rotation 21 a, 21 b which are directlyconnected with the axle 5. The sensors may be attached by means of apivot bearing (not shown). The level sensors 20 a, 20 b may also bemounted on pins as swivelling axes 21 a, 21 b which are pivotablyattached to the axle 5 or the laser core module 19 (cf. FIG. 3 and FIG.4), or any other known technique for pivotable attachment of the levelsensors 20 a 20 b may be utilized. The related axis of rotation 21 a, 21b is determined by the specific mechanical realization of the attachmentof the level sensors 20 a, 20 b.

It is emphasized that the rotating construction laser of FIG. 1 and FIG.2 is only shown for the purpose of exemplary, general technicalillustration for visualizing the general functional components of arotating construction laser and does not limit the scope of theinvention.

FIG. 3 shows a simplified illustration of a rotational constructionlaser according to the invention provided with a dual grade mechanism.Instead of the detailed illustration of a rotational construction laser1 as shown in FIG. 1 and FIG. 2, a laser core module 19 comprisingessential components of a rotational construction laser as exemplifiedin FIG. 1 and FIG. 2 is depicted in FIG. 3.

The dual grade mechanism comprises a first level sensor 20 a operable toindicate a rotation of the laser core module 19 around the X-axis and asecond level sensor 20 b operable to indicate a rotation of the lasercore module 19 around the Y-axis. The first and the second level sensors20 a, 20 b are designed to detect balance with respect to gravity. Thefirst level sensor 20 a is rotatable around a third axis of rotation 21a assigned to that first level sensor 20 a, and the second level sensor20 b is rotatable around a fourth axis of rotation 21 b assigned to thatsecond level sensor 20 b, rotation of the individual level sensors 20 a,2 b around their related swivelling axes 21 a, 21 b being mutuallyindependent, without affecting the reading of the other sensor not beingrotated.

The level sensors 20 a, 20 b may be attached by means of a pivot bearingdirectly to the laser core module 19. The level sensors may 20 a, 20 balso be mounted on a pin which is pivotably attached to the laser coremodule 19, or any other known technique for pivotable connection of thelevel sensors 20 a, 20 b with the laser core module 19 may be utilized.The related axis of rotation 21 a, 21 b is determined by the specificmechanical realization of the connection of the level sensors 20 a, 20 bwith the laser core module 19.

Preferably, the axis of rotation 21 a for the first level sensor 20 a isoriented in parallel to the X-axis of the outer pivoting mechanism fortilting the laser core module 19 in one direction, and the axis ofrotation 21 b for the second level sensor 20 b is oriented in parallelto the Y-axis of the outer pivoting mechanism for tilting the laser coremodule 19 in another direction.

The level sensors 20 a, 20 b may be provided as bubble vial sensors orspirit vials with a liquid in a receptacle. For precise, automated levelmeasurements and adjustments it is advantageous if the level sensors 20a, 20 b are provided with an opto-electronic readout system. Theopto-electronic readout system may comprise a light source, preferably alaser diode or a light-emitting diode (LED), illuminating the liquidenclosed together with the bubble in the level sensor. The light passingthrough the sensor and being deviated in different manners by regionsfilled with liquid and regions occupied by the bubble in the sensor isdetected by a light-sensitive device like a photodiode or a one- ortwo-dimensional diode or CCD array capable of detecting deviations froma symmetric distribution of the transmitted light. The light-sensitivedevice has the functionality of a linear image sensor. Any deviationfrom a symmetric transmitted light distribution may be scaled accordingto a requested resolution.

FIG. 4 illustrates a preferred embodiment of the rotating constructionlaser according to FIG. 3, wherein rotations around the swivelling axis21 a, 21 b of a level sensor 20 a, 20 b are actuated by a mechanicaldrive system comprising a bearing system 22 and a motor 23 connected tothe axis of rotation 21 a, 21 b for the level sensor 20 a, 20 b. Themechanical drive system can be attached directly onto the axis ofrotation 21 a, 21 b, or it could be connected to the swivelling axis 21a, 21 b by a lever arm with a linear drive mechanism such as a leadscrew, or any other variations of the drive mechanism may be utilized.The motor, typically an electric motor, may be operated by a controlunit.

It is further preferred that the mechanical drive system is providedwith a feedback mechanism 24 for recording and monitoring motor-actuatedrotation of the swivelling axis 21 a, 21 b. The feedback mechanism 24may comprise an optical encoder or any adequate detection device like alinear sensor attached between level sensor 20 a, 20 b and the lasercore module (19) operable to record the actuation of the swivelling axis21 a, 21 b scalable to an angle of rotation of the swivelling axis 21 a,21 b.

Preferably the electric motor 23 and the feedback mechanism 24 areoperated by a control unit 25 according to a closed-loop principle, i.e.information/data for motor actuation sent by the control unit 25 to theelectric motor 23 and positional data received by the control unit 25from the feedback mechanism 24 are correlated. If, for example, theelectric motor 23 is provided as a stepper motor, a number of steps ofthe motor can be translated into a corresponding angular rotation of theswivelling axis 21 a, 21 b. The advantage of such a closed-loopprinciple of operation is that the correlation between angular positionof the swivelling axis 21 a, 21 b and the operating position of themotor 23 is maintained at least as long electric power is notinterrupted.

The mechanical drive system may also be operated without feedbackcontrol or following an open-loop principle of operation, however uponcompromising the advantage of high repeatability and accuracy resultingfrom closed-loop operation under feedback: When using a stepper motorfor axis actuation, steps can be lost because of mechanical shock orfailure in the electronics. When operated according to an open-loopprinciple, information about such a loss of motor steps cannot befurther correlated with the actual axis position.

It is further advantageous if also the outer pivoting mechanism fortilting the laser core module 19, such as a pivoting system 4 asindicated in FIG. 1 and FIG. 2, is controlled by the control unit 25.

FIG. 5 a and FIG. 5 b illustrate the indications of bubble vial sensorsas an example of level sensors 20 a, 20 b upon a rotation of the lasercore module 19 together with the level sensors 20 a, 20 b around theY-axis by the outer pivoting system. It has to be understood that thedisplayed scales (−, 0, +) are only dedicated for purposes ofillustration without a numerical scaling. In an ideal situation, thelongitudinal axes of the level sensors 20 a, 20 b and the related axesof rotation 21 a, 21 b are perfectly aligned in parallel with the X- andY-axis of rotation of the laser core module 19, the X- and Y axis andconsequently also the axes of rotation 21 a, 21 b of the level sensors20 a, 20 b being orientated orthogonal to one another.

The lines 20 a′, 20 b′ show the indication of sensors 20 a, 20 b whenboth swivelling axes are set in zero position for the sensors 20 a, 20b, and the related sensors display balance with respect to gravity. Thebold lines 20 a″ and 20 b″ illustrate the sensor reading after arotation around swivelling axis 21 a on which sensor 20 a is mounted:The indication of sensor 20 a is still symmetric with respect to zeroreading. The bubble has only rolled by a certain amount (“transversalroll”) perpendicular to the sensor longitudinal axis in the tilt plane.In contrast the indication of sensor 20 b shows a departure from thezero value reading corresponding to the degree of tilt around axis 21 a,whereas, no “transversal roll” of the bubble has occurred, orientationwith respect to swivelling axis 21 b having not been changed.

The level sensor reading as illustrated in FIG. 5 a, FIG. 5 bcorresponds to the regular case that the longitudinal level sensor axis,corresponding to the sensor orientation of rotational sensitivity, isoriented perpendicular to the axis of rotation of the related levelsensor and the related axis (X or Y) of rotation by the outer pivotingsystem. In case that the level sensors would be mounted in aperpendicular orientation, i.e. with their longitudinal axis in parallelto the axis of rotation, the reading displayed in FIG. 5 a, FIG. 5 bwould correspond to a rotation about the X axis. Such an exchange ofsymmetry of sensor orientation would, however, only correspond to anexchange of sensitivity for rotations around the X- and Y-axis withoutleaving the scope of the invention.

1. A rotating construction laser comprising: a laser core moduleincluding: a laser unit for emitting a laser beam and rotation means forrotating the laser beam around an axis of rotation thus defining a laserbeam plane; an outer pivoting mechanism attached to the laser coremodule, the outer pivoting mechanism being operable to tilt the lasercore module around an X-axis as a first axis of rotation and around aY-axis as a second axis of rotation; and a dual grade mechanismincluding a first level sensor operable to indicate a rotation of thelaser core module around the X-axis and a second level sensor operableto indicate a rotation of the laser core module around the Y-axis, thefirst and the second level sensors being designed to detect balance withrespect to gravity, wherein: the first level sensor and the second levelsensor are individually attached to the laser core module; the firstlevel sensor is rotatable around a third axis of rotation; the secondlevel sensor is rotatable around a fourth axis of rotation; and arotation of the first and second level sensor around the related thirdand fourth axis of rotation is mutually independent.
 2. A rotatingconstruction laser according to claim 1, wherein the third and fourthaxis of rotation of the first and second level sensors are oriented inparallel to the X-axis and Y-axis, respectively, of rotation of the corelaser module.
 3. A rotating construction laser according to claim 1,wherein the third and fourth axis of rotation of the first and secondlevel sensors are oriented coaxially to the X-axis and Y-axis,respectively, of rotation of the core laser module.
 4. A rotatingconstruction laser according to claim 1, wherein the first and thesecond level sensors have a center of mass each, and the third and thefourth axis of rotation pass through the centers of mass of the firstlevel sensor and the second level sensor respectively.
 5. A rotatingconstruction laser according to claim 1, wherein the first and thesecond level sensors are provided as bubble vial sensors with a liquidand a bubble in a receptacle, the receptacle having a symmetrical andelongate, barrel-type shape.
 6. A rotating construction laser accordingto claim 5, wherein the first and the second level sensors are providedwith an opto-electronic readout system.
 7. A rotating construction laseraccording to claim 6, wherein the opto-electronic readout systemcomprises a light source illuminating the liquid enclosed together withthe bubble in the level sensor, the illuminating light passing throughthe sensor and being deviated as transmitted light in different mannersby regions filled with liquid and regions occupied by the bubble in thelevel sensor, wherein the opto-electronic read-out system furthercomprises, for a detection of the transmitted light, a light-sensitivedevice capable of detecting deviations from a symmetric distribution ofthe transmitted light.
 8. A rotating construction laser according toclaim 6, wherein the opto-electronic readout system comprises a laserdiode or a light-emitting diode illuminating the liquid enclosedtogether with the bubble in the level sensor, the illuminating lightpassing through the sensor and being deviated as transmitted light indifferent manners by regions filled with liquid and regions occupied bythe bubble in the level sensor, wherein the opto-electronic read-outsystem further comprises, for a detection of the transmitted light, alight-sensitive device capable of detecting deviations from a symmetricdistribution of the transmitted light, the light-sensitive device beinga photodiode or a one- or two-dimensional diode or CCD array
 9. Arotating construction laser according to claim 1, wherein rotationaround the third and/or fourth axis of rotation is operable by amechanical drive system, comprising a bearing system and a motor,connected to said axis of rotation.
 10. A rotating construction laseraccording to claim 9, wherein the mechanical drive system is providedwith a feedback mechanism and operable by a control unit for controllingmotor-actuated rotation around the third and/or fourth axis of rotation.11. A rotating construction laser according to claim 9, wherein themechanical drive system is provided with a feedback mechanism andoperable by a control unit for controlling motor-actuated rotationaround the third and/or fourth axis of rotation, wherein the feedbackmechanism comprises an optical encoder, which is provided as a linearsensor attached between level sensor and the laser core module operableto record the actuation of the swivelling axis scalable to an angle ofrotation of the swivelling axis, or as a rotary optical encoder.
 12. Arotating construction laser according to claim 10, wherein the outerpivoting mechanism is operable by the control unit.
 13. A rotatingconstruction laser according to claim 12, wherein the rotatingconstruction laser is further provided with a storage medium and acalibration data table stored in the storage medium, the calibrationdata table including: a first set of calibration data for a firstcalibration point obtained with the laser core module being mounted onan XY-axes tilt table with defined first values of tilt around theX-axis and the Y-axis; a second set of calibration data for the firstcalibration point obtained after activation of the mechanical drivesystem for the third and fourth axis of rotation for the level sensorsin order to rotate the level sensors into balance with respect togravity, the motor-actuated rotation around the third and fourth axisuntil reach of balance of the level sensors with respect to gravitybeing recorded by the feedback mechanism and stored in the storagemedium as data equivalent to angular rotations around the third andfourth axis, as the second set of calibration data.
 14. A rotatingconstruction laser according to claim 13, wherein the rotatingconstruction laser is further provided with a storage medium and acalibration data table stored in the storage medium, the calibrationdata table including: a first set of calibration data for a firstcalibration point obtained with the laser core module being mounted onan XY-axes tilt table with defined first values of tilt around theX-axis and the Y-axis; a second set of calibration data for the firstcalibration point obtained after activation of the mechanical drivesystem for the third and fourth axis of rotation for the level sensorsin order to rotate the level sensors into balance with respect togravity, the motor-actuated rotation around the third and fourth axisuntil reach of balance of the level sensors with respect to gravitybeing recorded by the feedback mechanism and stored in the storagemedium as data equivalent to angular rotations around the third andfourth axis, as the second set of calibration data; a first set ofcalibration data for a second calibration point obtained with the lasercore module being mounted on an XY-axes tilt table with defined secondvalues of tilt around the X-axis and the Y-axis; a second set ofcalibration data for the second calibration point obtained afteractivation of the mechanical drive system for the third and fourth axisof rotation for the level sensors in order to rotate the level sensorsinto balance with respect to gravity, the motor-actuated rotation aroundthe third and fourth axis until reach of balance of the level sensorswith respect to gravity being recorded by the feedback mechanism andstored in the storage medium as data equivalent to angular rotationsaround the third and fourth axis, as the second set of calibration data;and sets of calibration data for further calibration points.
 15. Arotating construction laser according to claim 13, wherein the rotatingconstruction laser is operable to generate a pre-defined laser beamplane for light emitted by the rotating construction laser by means of:actuating motors by the control unit and rotating level sensors aroundtheir related axes of rotation by pre-set angular amounts; actuating theouter pivoting system by the control unit and rotating the laser coremodule with the outer pivoting system around the X- and Y-axis untilreach of balance of the level sensors, signals of the level sensorsbeing acquired by the associated opto-electronic readout system and fedto the control unit; and maintaining rotation of the laser core moduleuntil signal readout indicating true horizon position of both levelsensors is reached.
 16. A rotating construction laser according to claim13, wherein the rotating construction laser is operable to generate apre-defined laser beam plane for light emitted by the rotatingconstruction laser by means of: actuating motors by the control unit androtating level sensors around their related axes of rotation by pre-setangular amounts equivalent to data retrieved from a stored calibrationdata table; actuating the outer pivoting system by the control unit androtating the laser core module with the outer pivoting system around theX- and Y-axis until reach of balance of the level sensors, signals ofthe level sensors being acquired by the associated opto-electronicreadout system and fed to the control unit; and maintaining rotation ofthe laser core module until signal readout indicating true horizonposition of both level sensors is reached.
 17. A rotating constructionlaser according to claim 15, wherein the rotating construction laser isprovided with an automatic re-adjustment functionality for restoring thelaser core module with the associated level sensors in a predefinedposition with respect to the gravitational force, by means of:registering deviations of readings of the level sensors from valuesindicating balance with respect to gravity; and re-adjustment of thelaser core module by tilting around the X- and Y-axis by means of theouter pivoting system operated by the control unit until reach ofbalance of the level sensors.
 18. A rotating construction laseraccording to claim 1, wherein the rotating construction laser isprovided as a self-levelling true horizon construction laser and arotation around the third and/or fourth axis of rotation and/or acalibration of a level sensor is manually operable, without operationunder an electronic control.
 19. A method of calibration of a dual grademechanism for a rotating construction laser according to claim 12,comprising the steps of: mounting the laser core module of the rotationconstruction laser on an XY-axes tilt table; setting and adjusting theXY-tilt table at first defined values of tilt around the X-axis and theY-axis and recording these values as a first set of calibration data fora first calibration point; activating the mechanical drive system forthe third and fourth axis of rotation for the level sensors in order torotate the level sensors into balance with respect to gravity; recordingwith the feedback mechanism the motor-actuated rotation around the thirdand fourth axis until reach of balance of the level sensors with respectto gravity; storing the recorded motor-actuated rotation around thethird and fourth axis as data equivalent to angular rotations aroundsaid third and fourth axis, as the second set of calibration data forthe first calibration point.
 20. A method according to to claim 19,further comprising the steps of: repeating the setting, activating,recording and storing steps for second defined values of tilt around theX-axis and the Y-axis in order to obtain first and second sets ofcalibration data for a second point of calibration; further repeatingthe setting, activating, recording and storing steps for obtaining setsof calibration data for further calibration points; and storing the setsof calibration data for the calibration points on a storage medium. 21.A method of generating a pre-defined laser beam plane, with a predefinedtilt with respect to a horizontal plane, for light emitted by a rotatingconstruction laser according to claim 1, wherein: the first and thesecond level sensors are rotated relative to the core module aroundtheir related third and fourth axis of rotation by pre-set angularamounts, dependent on the pre-defined laser beam plane; and the lasercore module is rotated by the outer pivoting system around the X- andY-axis until reach of balance of the first and second level sensorindicated by signal readout of the first and second level sensorcorresponding to true horizon position.
 22. A method according to claim21, wherein: motors are actuated by the control unit, and level sensorsare rotated around their related axes of rotation by pre-set angularamounts; the outer pivoting system is actuated by the control unit andthe laser core module is rotated by the outer pivoting system around theX- and Y-axis until reach of balance of the level sensors, wherebysignals of the level sensors are acquired by the associatedopto-electronic readout system and fed to the control unit, and rotationof the laser core module is maintained until signal readout indicatingtrue horizon position of both level sensors is reached.
 23. A methodaccording to claim 22, wherein: motors are actuated by the control unit,and level sensors are rotated around their related axes of rotation bypre-set angular amounts equivalent to data retrieved from a storedcalibration data table are rotated around their related swivelling axes;the outer pivoting system is actuated by the control unit and the lasercore module is rotated by the outer pivoting system around the X- andY-axis until reach of balance of the level sensors, whereby signals ofthe level sensors are acquired by the associated opto-electronic readoutsystem and fed to the control unit, and rotation of the laser coremodule is maintained until signal readout indicating true horizonposition of both level sensors is reached.
 24. A method according toclaim 22 in order to generate a vertical laser beam plane, wherein: thefirst or the second level level sensor is rotated relative to the coremodule around the related third or fourth axis of rotation by an amountaccording to a 90° turn whereas the other level sensor is maintained ina 0° turn position; and the laser core module is around the X- and/orY-axis until reach of signal readout of both the first and second levelsensor corresponding to true horizon position.